A wide variety of electrical terminal blocks are known. Most involve screw connectors in which a wire is wrapped around a screw and the screw is tightened to secure the connection. Others, those illustrated in U.S. Pat. Nos. 4,077,696 and 3,812,453 for example, have screws which activate a clamping piece which captures the wire and secures the electrical connection.
The screw-type terminal blocks are frequently rather bulky, resulting in a waste of printed circuit board space, and are labor intensive in that they require the wire to be wrapped around a screw which is then manually tightened by means of a screwdriver. They also suffer from the additional deficiency that they can be overtightened with the result that the wire is squeezed out from between the screw head and the opposing contact element. This is a particular problem with multistranded wire.
Various approaches to screwless terminals have suffered from the difficulties that the terminals could not be manufactured by high speed automated assembly methods, they were rather expensive, they could handle only a limited range of wire sizes, wire retention forces were frequently inadequate, they required one or more tools to insert or remove wires, and the designs produced long term fatigue stress in plastic or metal parts employed in such terminals.
In view of these problems it would be very desirable to have a simple inexpensive screwless connector having the ability to accommodate a wide range of wire diameters and also having strong wire retention forces to hold a connected wire securely.